A. Field of the Invention
The present invention relates in general to geodesy, cartography and computer technology, and in particular to positioning systems, digital orthophotographs and digital terrain elevation data, and Geographic Information Systems.
B. Prior Art
A variety of computerized information display systems have been developed to function as simulators, vehicular obstacle avoidance systems, and vehicle tracking systems. Such systems use computer generated imagery based on data sets generated either from digitized contour maps or symbolic maps or combinations of both. Typically, such systems include some method of determining the mode of transportation's location in space (utilizing "dead-reckoning" techniques using on-board sensors, transmitting beacons, a satellite positioning system, or combinations of these) and a method of displaying/updating the mode of transportation's location on a digitized symbolic map or chart using computer graphics.
The major drawback in the aforementioned systems is the lack of realistic visual feedback displayed on a graphics monitor along with the mode of transportation's position. Artificially created geographic data (such as is found in flight simulators) or data derived from digitized cartographic contour/elevation maps lack the realism and true photographic detail of the geographic surroundings, such as vegetation and man made structures such as buildings, powerlines, etc. The use of symbolic maps or the addition of symbols to digitized contour maps can provide some information with respect to man made structures and vegetation, but to provide information density comparable to what would be observed by directly looking at a portion of the earth with the naked eye is not practically feasible by symbolic representation. In addition to the time intensive and costly process of making symbolic maps, many features cannot be accurately placed because of cartographic displacement caused by adjacent symbols.
At present, there is no effective way operators of moving modes of transportation such as ships, aircraft or land vehicles can visually ascertain their and each other's positions, if there is no visibility, and be alerted to the proximity of obstructions. This was clearly demonstrated by the environmental disaster caused when the ship, the EXXON VALDEZ, ran aground at night in March of 1989 after leaving Valdez, Alaska and leaked its load of approximately 11,000,000 gallons of crude oil upon the ocean. Other examples are the December 1990 collision of two Northwest Airlines passenger jets at the Detroit, Mich. airport in a dense fog and the collision on Feb. 1, 1991 at Los Angeles International airport at night between a U.S. Air Boeing 737 and an Airwest commuter jet aircraft. In the former case, one airliner was lost and taxied on to an active runway and was hit by the other airliner as it was taking off causing eight deaths, injuries and much damage. In the latter case, the U.S. Air Boeing 737 was mistakenly cleared to land on the runway being used by the Airwest commuter aircraft previously cleared for takeoff. The collision caused 30 deaths.
In other to provide background information so that the invention may be completely understood and appreciated in its proper context, and how it can prevent accidents like the ones described above, reference may be made to a number of prior art patents as follows:
U.S. Pat. Nos. 4,837,700; 4,835,537; 4,682,160 and 4,829,304.
A number of patents such as typified by U.S. Pat. No 4,837,700, to Ando et al, discloses a road vehicle navigation system using a Global Positioning System (GPS) receiver and odometer, angular rate, and geomagnetic sensors. A digitized map of the area is also displayed and scrolled by computer and the operator's position on the map is displayed as determined from the sensors or GPS signals. Digitized symbolic maps or charts used with the above patent, and with vehicle, aircraft, and ship navigation and positioning systems in general, suffer from a number of deficiencies. Symbolic maps or charts show only selected features and only as symbols, and the spaces between the symbols are left blank. Additionally, many features are not accurately placed on symbolic maps because of cartographic displacement caused by adjacent symbols. The digital maps used with the aforementioned systems make little, or no use of different digital data layers to develop (in a dynamic fashion) statistics and make new digital maps of the surrounding environment as position changes, or use geo-referenced terrain elevations to assess distances from obstacles and generate perspective views for added realism. The above patent makes no mention of transformations that must be made when displaying GPS geographic coordinates based on various X-Y map projections and spheroids. This can be a source of error.
Remotely sensed digital satellite image data of the earth can also be used as a map or chart and the operator's position displayed thereon through the use of GPS signals. The image data are fitted to ground by rubber sheeting or warping the common image points in the image and their counterparts on an existing map or chart using their known positions on the ground. This gives a good fit at the registration points, but as one moves away from the registration points accuracy falls off. Additionally, no provision is made to correct for relief displacement. These errors, and the small scale, limit the use of satellite imagery as a map or chart.
U.S. Pat. No. 4,835,537, to Manion, discloses an aircraft warning and avoidance system. All mobile obstacles whether aircraft or vehicles on the ground must be outfitted with radio telemetry devices that receive various TACAN and LORAN and preferably GPS positioning information and transmit their position based upon these incoming signals. Natural obstacles such as mountain peaks or man made objects such as radio towers can also be outfitted with radio telemetry devices that broadcast their location. The pilot of an aircraft is shown a symbolic view of the instrumented objects around the pilot and audibly warned of impending collisions if the present course is maintained. The problem with this system is that not all aircraft and vehicles on the ground may always be instrumented with the costly telemetry transceivers. In addition, it would not be economically practical to instrument all natural objects with the transmitters. The cost of maintaining the instruments at each site in working order also needs to be considered. Distances are calculated between instrumented objects, fixed or mobile (transmitting their respective coordinates), based upon latitude and longitude of the mode of transportation; rather than reduction to a map or chart coordinate system. Such an approach could lead to inaccuracies along the equator or in polar regions due to earth curvature. Again, as with the above patents, only a symbolic display is shown of the surrounding environment, and not realistic geo-referenced photographic quality imagery to guide the operator.
U.S. Pat. Nos. 4,682,160, to Beckwith et. al, and 4,829,304 to Baird, introduce a new component to navigation and aircraft navigation in particular, the use of digital geo-referenced terrain data. The former uses terrain elevations to generate a shaded relief perspective view image in real time of the terrain, in consonance with pitch, roll and yaw of the aircraft, over which the aircraft is flying. The imagery displayed however, is synthetic as it is derived by computer graphics shading techniques based upon adjacent elevation differences and does not show the landscape in true photographic detail, which is a primary object of the current invention. The latter uses various aircraft instruments such as a barometer, radar altimeter readings, and estimated position from the onboard navigation system to compare a sensed profile of digital terrain data to a corresponding profile of stored digital terrain data. When a match is found, the onboard navigation system is updated with the new position. Thus the piloted or automatic guidance (pilotless) mode of transportation is able to navigate and avoid obstacles. Again these two schemes use onboard sensors to determine position. Sensors accumulate error as distances increase between correlation points. Where there are no terrain differences, as over water, both systems would become unreliable as there would be no terrain profiles with which to correlate the stored terrain data. Additionally, in the latter system, barometric pressure can be influenced by current weather conditions and gusts of wind can disorient the mode of transportation and give erroneous radar altimeter readings. This makes it difficult or impossible to obtain a reliable terrain profile with which to make a correlation with stored terrain data. Again, these systems do not show the pilot's position in a visual photographic image of the terrain or water over which the aircraft is flying.
Present day training simulators for various modes of transportation, particularly aircraft flight simulators and warfare mission planning systems and other devices such as video games, use artificially generated imagery for training or entertainment. Computer simulated imagery detracts from the simulation and lacks the realism of photographic imagery.
Geographic Information Systems (GIS) technology is now used with user input parameters to model various geo-referenced data sets in order to gain new information about the environmental relationships between various data sets. This is done in a static mode at a single site. In a dynamic situation such as a forest fire, it may not be obvious what to model at a distant office site based upon untimely user reported conditions in order to forecast the spread of the fire and the subsequent decisions that would have to be made to evacuate personnel and to allocate both personnel and resources to fight the fire.